1. Field of the Invention
The present invention relates to the sliders and the head gimbal assemblies of a hard disk drive.
2. Background Information
Hard disk drives contain one or more magnetic heads that are coupled to rotating disks. The heads write and read information by magnetizing and sensing the magnetic fields of the disk surfaces. Magnetic heads have been developed that have a write element for magnetizing the disks and a separate read element for sensing the magnetic field of the disks. The read element is typically constructed from a magneto-resistive material with a resistance that varies with the magnetic fields of the disk. Heads with magneto-resistive read elements are commonly referred to as magneto-resistive (MR) heads.
Each head is embedded in a slider, which is attached to a flexure arm to create a subassembly commonly referred to as a head gimbal assembly (HGA). The HGA's are attached to an actuator arm. The actuator arm has a voice coil motor that can move the heads across the surfaces of the disks.
Information is stored in radial tracks that extend across the surfaces of each disk. Each track is typically divided up into a number of segments or sectors. The voice coil motor and actuator arm can move the heads to different tracks of the disks and to different sectors of each track.
A suspension interconnect extends along the length of the flexure arm and connects the head to a preamplifier. The suspension interconnect typically comprises a pair of conductive write traces and a pair of conductive read traces. One pair of traces, such as the read traces, extend down one side of the flexure arm to the head and the remaining pair of traces extends down the other side of the flexure arm to the head.
The number of Tracks Per Inch (TPI) formed on the surface of hard disk drives is rapidly increasing, leading to smaller and smaller track positional tolerances. The track position tolerance, or the offset of the read-write head from a track, is monitored by a signal known as the head Positional Error Signal (PES). Reading a track successfully usually requires minimizing read-write head PES occurrences. The allowable level of PES is becoming smaller and smaller. A substantial portion of the PES is caused by disk vibration.
Track Mis-Registration (TMR) occurs when a read-write head loses the track registration. This occurs when the disk surface bends up or down. TMR is often a statistical measure of the positional error between a read-write head and the center of an accessed track.
One approach to reducing TMR uses the head gimbal assemblies to provide a radial motion capability, which lowers the Track Mis-Registration (TMR) due to disk vibration. The head gimbal assembly, including a biased load beam, creates a roll center (also known as a dimple center), which provides a radial motion capability as the load beam moves vertically due to disk vibration. This allows sliders to move in a radial direction as well as in a vertical direction with respect to the disks, reducing off-track motion due to disk vibration.
This approach has some problems. An air bearing forms between the slider face and the disk surface. The slider face is tilted near the disk surface when it is flat. The air bearing becomes non-uniform when the disk surface is flat, adding new mechanical instabilities into the system.
An alternative prior art head gimbal assembly provides a slider mounted so that it pivots in the radially oriented plane about the effective roll axis, which is located within the disk. This scheme does not cause a non-uniform air bearing when the disk surface is flat. However, the way the effective roll axis is placed inside the disk requires a more complex mechanical coupling between the slider support assembly and the slider. This complex mechanical coupling has a greater probability of mechanical failure, tending to increase manufacturing expenses and to reduce hard disk drive life expectancy.
Accordingly, there exists a need for head gimbal assembly mechanisms that may provide a stable air bearing, and which may follow a track when a disk surface bends. These head gimbal assembly mechanisms also need to be inexpensive to manufacture.